1. Field of the Invention
The present invention generally pertains to monitoring devices for indicating certain conditions or properties of a material. More particularly, it pertains to a novel and improved method and apparatus for preventing shorting of monitoring electrodes adapted for use in foam scrubbing apparatuses of the type which are utilized for separating particles and gaseous contaminants from a gaseous medium.
2. Description of the Prior Art
In the pollution abatement field, several well-known categories of apparatuses are especially adapted for use in separating particles from a flowing fluid stream. One of these known categories, for instance, utilizes a foam material which serves to filter particulate matter and absorb gaseous contaminants from a flowing gas stream. In such a type of apparatus, the gas which contains the particulate matter and dissolved gaseous contaminants flows through a channel which is charged with a layer of foam material positioned between a dirty gas inlet and a clean gas outlet. As the gas is forced to travel through the foam, such foam acts to remove particulate matter as well as dissolved gaseous contaminants. The aforedescribed separating apparatus is of the type generally referred to as a foam scrubber, such as the kind disclosed in U.S. Pat. No. 3,616,610.
Although the foregoing type of scrubber arrangement serves to clean a variety of gases, particularly those issuing from industrial operations, they do not always entirely satisfactorily perform their operations. One reason for such performance is that it is somewhat difficult to maintain an optimum foam layer composition; especially whenever synthetic based foaming agents are utilized. A conventional approach taken to insure proper foam layer density is through the use of a monitoring system for measuring foam layer height. Typically, a generally elongated rod-like electrode sensor is mounted by a plastic holder or the like so as to be inserted into the scrubber chamber for exposure to the foam. It is arranged to sense the height of the foam layer and is connected by conventional electrical means to a foam generator. Whenever the foam layer is too low, for example, the sensor generates a signal to a foam generator for actuating the latter such that more foam is supplied to the layer so as to maintain optimum density.
A particular disadvantage which sometimes occurs in the operation of such a monitoring system is the malfunctioning of the electrodes. Consequently, the monitoring system would be unable to detect the level of foam that is charged within the channel and, accordingly, fail to perform its intended operation in that the foam may not separate a sufficient quantity of particulate and dissolved gaseous contaminants from the dirty gas. Such malfunctioning may often arise by reason of the fact that the electrodes are subject to accumulation thereon of foreign particles. It has been determined that, regardless of whether the accumulated foreign particles are conductive or non-conductive, they become saturated with the foam solution. Such accumulation of saturated material may result in the sensing electrode being electrically shorted by virtue of the material creating an electrical path for current to flow from the electrode to a chamber wall to which such electrode is operatively connected. Consequently, of course, the electrode becomes inoperative and the monitoring system fails to perform its intended function.
Although there are known forms of conventional apparatuses which, in general, serve to protect against buildup of particles or the like on sensor probes, they are, in general, more complicated, expensive, or unsuitable for application in foam scrubber units. For instance, U.S. Pat. No. 2,626,620, describes a system wherein a portion of spray water is passed to sensor probes, which probes are surrounded by screens and sheaths. This particular system would not appear to be capable of protecting an electrode in a foam scrubber by reason of the fact that foam saturated foreign particles would seemingly still be able to accumulate on the sensor and screen. Other known approaches of the prior art to protect electrical sensors normally employ shield devices which partially surround the sensors. However, this particular arrangement would, likewise, appear to be subject to the accumulation of foreign material which might cause shorting of an electrode sensor in a foam scrubber apparatus.
While other known procedures may force air from the outside of a chamber to the inside of the chamber, along a probe, such procedures require a relatively enormous volume of a fluid medium. Consequently, such procedures are relatively expensive to successfully operate. Consequently, heretofore known protection devices for electrical sensors do not appear particularly adapted for use in economically and easily preventing build-up of saturated foreign particles on electrode sensors which are exposed to foam in a foam scrubber apparatus.